Foam detector for concentrator attachment for gas chromatograph

ABSTRACT

A foam detector ( 10 ) generally including a pair of leads ( 14, 16 ) positioned adjacent to a surface layer ( 26 ) of a fluid ( 24 ) so that foam created on a surface layer ( 26 ) of the fluid ( 24 ) contacts at least one lead and sends a signal to a controller ( 18 ) connected to the leads ( 14, 16 ).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to foam detectors and, moreparticularly, to foam detectors used in conjunction with a concentratorfor gas chromatographs.

[0003] 2. Brief Description of the Prior Art

[0004] When a gas is diffused through a fluid, bubbles can form andcollect on a surface layer of the fluid. The accumulation of bubbles iscommonly referred to as foam.

[0005] In some applications, such as in gas chromatography samplepreparation, sample vessels are used to extract volatile organics fromwater samples or the like. A pressurized sparging gas is introduced intothe water sample and diffuses through the water sample. The volatileorganics are carried out of the water sample by the sparging gas andconcentrated by a trap in a sample concentrator. The concentratedorganics are then released from the trap and passed to an analyzinginstrument, such as a gas chromatograph. If the bubbling action of thesparging gas creates foam over the surface layer of the water sample,the foam may or may not be contained or dissipated by a bubble breakerdefined by the sample vessel. The presence of foam can lead to erroneousmeasurements or contamination of the sample concentrator. U.S. Pat. No.4,910,996 to Pfisterer et al. discusses foaming problems in gaschromatographs used in beer processing. To combat the foam problem, thePfisterer patent discloses using pressure regulators to pressurize abeer sample and prevent outgassing of the beer. However, if outgassingdoes occur, there is no way to test for the presence of the foam priorto the advancement of the concentrated prepared sample into internaltubing housed within the sample concentrator or the gas chromatograph.

[0006] Another problem not addressed by the prior art is the process ofcleaning the sample concentrator if inadvertent contamination of theinternal tubing does occur. Cleaning a contaminated sample concentratorgenerally takes a few weeks and includes the steps of taking thecontaminated sample concentrator offline, shipping the sampleconcentrator to a cleaning facility, and reinstalling the cleaned sampleconcentrator.

SUMMARY OF THE INVENTION

[0007] To help obviate the disadvantages of the prior art, the presentinvention generally includes a device for detecting the presence of foampositioned adjacent to a surface layer of a fluid. The device generallyincludes a first lead positioned adjacent to the surface layer of thefluid, a second lead positioned adjacent to the surface layer of thefluid and spaced apart or electrically insulated from the first lead,and a controller connected to the first lead and the second lead. Thefirst lead and the second lead may be thermocouples, with the first leadspaced at a further linear distance from the surface layer of the fluidthan the second lead. Alternatively, the first lead and the second leadmay be made from an electrically conductive material.

[0008] A method for the detection of foam positioned adjacent to asurface layer of a fluid is also provided. The method generally includesthe steps of positioning a pair of leads adjacent to the surface layerof the fluid, with the leads each spaced apart or electrically insulatedfrom one another. Additional steps include forming foam on the surfacelayer of the fluid, bringing the foam in physical contact with one orboth of the pair of leads after the step of forming foam on the surfaceof the fluid, and registering a presence of the foam. Still furthersteps include (1) reducing the temperature of one of the leads after thestep of bringing the foam in physical contact with one of the pair ofleads and (2) flowing an electrical current from one of the pair ofleads, through the foam, to another of the pair of leads, after the stepof bringing the foam in physical contact with both of the pair of leads.

[0009] One particular application of the present invention is a systemfor detecting the presence of foam in gas chromatography. The systemgenerally includes a gas chromatograph, a sample concentrator, such as amodular sample concentrator fluidly connected to the gas chromatograh, asample vessel defining an internal cavity fluidly connected to thesample concentrator, a pair of leads positioned, in the internal cavityof the sample vessel, and a controller connected to the pair of leads. Afluid and foam may also be included, the fluid contained in the internalcavity of the sample vessel and the foam positioned on a surface layerof the fluid, wherein the foam physically touches at least one of thepair of leads. The modular sample concentrator may generally include afirst body section housing, internal tubing, and a second body sectionhousing control electronics, wherein the first body section and thesecond body section are removably connected to one another. Cleaning thesample concentrator includes the steps of removing a contaminated firstbody section from a second body section, replacing the contaminatedfirst body section with a clean first body section, and resumingoperation of the sample concentrator.

[0010] The present invention allows foam to be detected by one or bothof the pair of leads, through the controller, and alert the operator sothat the system can be shut down or continue to operate, depending onpreprogram settings. Moreover, if the sample concentrator iscontaminated by foam, the sample concentrator can be easily and quicklyreturned to operative service.

[0011] These and other advantages of the present invention will beclarified in the description of the preferred embodiments taken togetherwith the attached drawings in which like reference numerals representlike elements throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a sectional view of a first embodiment foam detectorassembly according to the present invention;

[0013]FIG. 2 is a sectional view of a second embodiment foam detectorassembly according to the present invention;

[0014]FIG. 3 is a first end view of a modular sample concentratoraccording to the present invention;

[0015]FIG. 4 is a side view of the modular sample concentrator shown inFIG. 3; and

[0016]FIG. 5 is a second end view of the modular sample concentratorshown in FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The Applicants previously filed U.S. Provisional PatentApplication Serial Nos. 60/188,639 and 60/224,242, which are bothincorporated herein by reference in their entireties.

[0018] A foam detector 10 according to a first embodiment of the presentinvention is shown in FIG. 1. The first embodiment foam detector 10shown in FIG. 1 is shown in conjunction with a gas chromatography samplevessel 12 to help aid in the understanding of the present invention, butgas chromatography is only one possible type of application.

[0019] As shown in FIG. 1, the foam detector 10 generally includes afirst lead 14, a second lead 16 electrically insulated from the firstlead 14, and a controller 18 connected to the first lead 14 and thesecond lead 16. In the particular application shown in FIG. 1, thesample vessel 12 defines an internal cavity 20 and a bubble breaker 22,the internal cavity 20 receiving a fluid 24 having a surface layer 26.Moreover, the first lead 14 is a sensor wire 32 and the second lead 16is a dip tube 30, which is electrically grounded 28.

[0020] The sample vessel 12 forms a first end 34 and a second end 36,and is generally made from glass or other electrically non-conductivematerial. A first collar 38 is preferably positioned adjacent to thefirst end 34 of the sample vessel 12 for receiving a housing 40. Thehousing 40 is generally a hollow structure defining an evacuation branch42, a fill branch 44 with an optional septum retainer to allow forsyringe injections, and a dip tube passageway 46, with the dip tubepassageway 46 receiving the dip tube 30. An optional sensor conduit 48is preferably fluidly connected to the dip tube passageway 46, andpreferably extends away from the housing 40 at an angle α generallybetween 1 and 179 degrees. However, the sensor conduit 48 is notrequired if the housing 40 defines a sealed orifice or is otherwiseconfigured to receive a sensor wire 32, discussed below. A second collar50, configured to provide a fluid seal with the dip tube 30, is alsopositioned adjacent to the housing 40. As previously stated, the diptube 30 preferably extends through the dip tube passageway 46 defined bythe housing 40 and continues to extend in a direction away from thesample vessel 12 and the housing 40.

[0021] One end of the sensor wire 32 extends through the sensor conduit48 connected to the housing 40 and is fluidly sealed to the housing 40by a third collar 52. The other end of the sensor wire 32 iselectrically connected to a vessel ferrule 56. The sensor wire 32 ispreferably electrically conductive, such as a 0.010 inch diameter wiremade from stainless steel or other suitable electrically conductivematerial. The vespel ferrule 56 is generally made from plastic andmetal, metal, or any other suitable material or materials. A carrierwire 58, preferably made from 22-gauge copper or any other diameter ofsuitable material, is also connected to the vespel ferrule 56. Anelectrically insulated material 60, such as PEEK brand heat shrinktubing, preferably encompasses all of the electrically conductive parts.More specifically, the PEEK brand heat shrink tubing is sealinglycaptured in the vespel ferrule 56 and extends along with the sensor wire32 through the sensor conduit 48, the dip tube passageway 46 in thehousing 40, and into the internal cavity 20 defined by the sample vessel12, terminating above the bubble breaker 22. The sensor wire 32 extendsout of the electrically non-conductive material 60 and is bent back overthe material 60. An exposed end 62 of the sensor wire 32 is arranged asnot to contact the dip tube 30, which is preferably electricallygrounded.

[0022] With continuing reference to FIG. 1, a sparging gas 64 flowsthrough the dip tube 30 in the direction shown by arrow A1 and into thesecond end 36 of the sample vessel 12. The sparging gas 64 percolatesthrough the fluid 24 introduced into the sample vessel 12, capturesvolatile organic analytes or other substances from the fluid 24, andcarries the analytes out of the sample vessel 12 through the evacuationbranch 42. If foam forms on the surface layer 26 of the fluid 24, thefoam rises in a direction indicated by arrow A2 and enters the bubblebreaker 22. When foam moves up beyond the bubble breaker 22 and contactsthe exposed end 62 of the sensor wire 32 and the dip tube 30, current isdrawn through the sensor wire 32 as the electrical discontinuity presentbetween the spaced apart sensor wire 32 and dip tube 30 is closed by thefoam. This current, produced by a current source 66 in the controller18, is sensed by the controller 18 and a signal is generated indicativeof foam beyond the bubble breaker 22. The signal passes though anisolation circuit 68 and foam detection logic is applied. The controller18 is programmed to respond to the signal in a way specified by the userwhich may, for example, include shutting down the gas chromatographyapplication to allow cleaning of sample vessel 12. The current source 66is designed so that when foam contacts the sensor wire 32, current flowsin a range of approximately 1-10 micro amps. The current is controlledby the voltages applied across the sensor wire 32 in the dip tube 30 andthe additional series resistance. The current is so limited to minimizehydrolysis of the fluid 24 in the sample vessel 12.

[0023] A foam detector 10′ according to a second embodiment of thepresent invention is shown in FIG. 2. The second embodiment foamdetector 10′ is also shown in connection with a gas chromatographyapplication, but other applications are also contemplated. Moreover,when compared to FIG. 1, like parts in FIG. 2 are represented by likereference numerals.

[0024] In the second embodiment foam detector 10′, as shown in FIG. 2,the housing 40′ preferably has two sensor conduits 48, 48′. The firstlead 14′, such as a first thermocouple 70, is inserted through thesensor conduit 48, is sealed by fourth collar 54, and extends away fromthe housing 40′ in a direction A3 toward the bubble breaker 22. Thesecond lead 16′, such as a second thermocouple 72, is inserted throughthe second sensor conduit 48′, is sealed by a second fourth collar 54,and also extends away from the housing 40′ in a direction toward thebubble breaker 22. The first lead 14′ extends further away from thehousing 40′ than the second lead 16′, so that the first lead 14′ isspaced closer to the bubble breaker 22 than the second lead 16′.

[0025] With continuing reference to FIG. 2, sparging gas 64 flowsthrough the sample vessel 12 in the direction of arrow A3 through thefluid 24. As the sparging gas 64 percolates through the fluid 24,volatile organic analytes or other substances are captured from thefluid 24 and exit the sample vessel 12 through a dip tube 30 (FIG. 1)which extends through the housing 40′. If foam forms on the surfacelayer 26 of the fluid 24, the foam rises in a direction indicated byarrow A4 and enters the bubble breaker 22. When foam moves up beyond thebubble breaker 22 and contacts the first lead 14′, which is spacedcloser to the bubble breaker 22 than the second lead 16′, the foam coolsthe first lead 14′, which, in this embodiment, is a first thermocouple70. The cooling creates a temperature differential between the firstthermocouple 70 and the second thermocouple 72. Any temperaturedifference between the first thermocouple 70 and the second thermocouple72 results in a corresponding electrical differential. The electricaldifferential is measured by a controller 18′ having a balanced bridgecircuit 74 which is zeroed at startup using an autotear circuit 76. Thebalance bridge circuit 74 compares the electrical output of the firstthermocouple 70 and the electrical output of the second thermocouple 72.The comparison of the first thermocouple 70 and the second thermocouple72 can be adjusted using a user deviation circuit 78. The deviationcircuit 78 can be used to correct for drift and other problems.Thermocouples 70, 72 are preferred in this embodiment because thethermocouples 70, 72 are in the same thermal environment in theirrespective electrical outputs are generally equal to one another.Therefore, if both the first and second thermocouples 70, 72 are heatedor cooled equally, both will produce a zero output voltage or an outputvoltage normalized to zero.

[0026] If the difference between the electrical output of the firstthermocouple 70 and the second thermocouple 72 exceeds the deviationentered by the user, the process or operation stops, holds, or shutsdown, thereby preventing contamination and erroneous results. However,if the difference between the electrical output of the firstthermocouple 70 and the second thermocouple 72 is within the tolerancesset by the user, the process keeps running for the desired allottedperiod of time, stops, and the comparison zeroed itself. Only a suddenrise or fall in voltage outside the set tolerances causes shutdown.Continuous slow drift is neutralized by a periodic rezeroing of theoutput signals of the first and second thermocouples 70, 72.

[0027] In the unlikely event that the first and second embodiment foamdetectors 10, 10′ become incapacitated due to wear, a modular sampleconcentrator 80, shown in FIGS. 3-5, can be used either in conjunctionwith the first and second embodiment foam detectors 10, 10′ or withoutthe first and second embodiment foam detectors 10, 10′. As shown in FIG.3, the modular sample concentrator 80 generally includes a first bodysection 82 removably connected to a second body section 84. As showngenerally in FIGS. 3 and 5, and with more detail in FIG. 4, the firstbody section 82 preferably houses internal tubing 85 which is fluidlyconnected at one end 86 to a sample vessel 12 and is fluidly connectedat a second end 88 to a gas chromatograph 90. Referring again to FIG. 3,the second body section 84 houses electronic control circuitry and mayalso contain an input control panel 92. The first and second bodysections 82, 84 are preferably electrically connected to each other viaa wiring harness 94, an integrated circuit board 96, and one or morespring loaded attachment posts 98.

[0028] Referring generally to FIGS. 3-5, one method of repairing themodular sample concentrator 80 includes the steps of operating themodular sample concentrator 80, allowing the first body section 82internal tubing 85 to become contaminated, stopping the modular sampleconcentrator 80, removing the first body section 82, replacing theremoved first body section 82 with another first body section 82 havingclean internal tubing 85, restarting the modular sample concentrator 80,and cleaning the contaminated first body section 82. This method allowsthe modular sample concentrator 80 to become operational quickly,without taking the entire modular sample concentrator 80 offline for oneor more days.

[0029] The invention has been described with reference to the preferredembodiments. Obvious modifications and alterations will occur to othersupon reading and understanding the preceding detailed description. It isintended that the invention be construed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

I claim:
 1. A system for detecting the presence of foam positionedadjacent to a surface of a fluid in a sample vessel for a gaschromatograph, the system comprising: a gas chromatograph and a samplevessel in fluid communication; a first conductive lead positioned in thesample vessel adjacent to the surface layer of the fluid; a secondconductive lead positioned in the sample vessel adjacent to the surfacelayer of the fluid; and a controller connected to the first conductivelead and the second conductive lead.
 2. The device as claimed in claim 1wherein the first conductive lead is spaced away from the secondconductive lead.
 3. The device as claimed in claim 1 wherein the firstconductive lead is a thermocouple.
 4. The device as claimed in claim 1wherein the first conductive lead is spaced at a further linear distancefrom the foam than the second conductive lead.
 5. The device as claimedin claim 1 wherein the controller is a balanced bridge circuit.
 6. Thedevice as claimed in claim 5 wherein the controller further comprises anauto tear circuit and a deviation circuit.
 7. The device as claimed inclaim 1 wherein the first conductive lead is made from an electricallyor thermic conductive material.
 8. The device as claimed in claim 7wherein the second conductive lead is an electrically grounded dip tube.9. The device as claimed in claim 7 wherein the first conductive lead iselectrically grounded.
 10. The device as claimed in claim 1 wherein thecontroller is a current source and an isolation circuit.
 11. A methodfor the detection of foam positioned adjacent to a surface of a fluidcomprising the steps of: providing a sample vessel connected to a gaschromatograph; positioning a pair of conductive leads inside the samplevessel, adjacent to the surface of the fluid; forming foam on thesurface of the fluid; and registering a presence of the foam.
 12. Themethod as claimed in claim 11 further comprising the step of spacing thepair of conductive leads away from one another after the step ofpositioning a pair of conductive leads adjacent to the surface of thefluid.
 13. The method as claimed in claim 11 further comprising the stepof bringing the foam in physical contact with one of the pair ofconductive leads after the step of forming foam on the surface of thefluid.
 14. The method as claimed in claim 13 further comprising the stepof reducing the temperature of one of the pair of conductive leads afterthe step of bringing the foam in physical contact with one of the pairof conductive leads.
 15. The method as claimed in claimed in claim 11further comprising the step of bringing the foam in physical contactwith both of the pair of conductive leads after the step of forming foamon the surface of the fluid.
 16. The method as claimed in claim 15further comprising the step of flowing an electrical current from one ofthe pair of conductive leads, through the foam, and to another of thepair of conductive leads after the step of bringing the foam in physicalcontact with both of the pair of conductive leads. a modular sampleconcentrator fluidly connected to the gas chromatograph, the modularsample concentrator comprising a first body section and a second bodysection, the first body section having internal tubing housed therein,the second body section having electronic control circuitry housedtherein, and the first body section and the second body sectionremoveably connected to each other; a sample vessel defining an internalcavity, the internal cavity fluidly connected to the internal tubinghoused in the first body section of the modular sample concentrator; apair of conductive leads positioned in the internal cavity of the samplevessel; and a controller connected to the pair of conductive leads. 18.The device as claimed in claim 17 wherein one of the pair of conductiveleads is a thermocouple.
 19. The device as claimed in claim 17 whereinone of the pair of conductive leads is made from an electricallyconductive material.
 20. The device as claimed in claim 17 furthercomprising a fluid and foam, the fluid contained in the internal cavityof the sample vessel and the foam positioned on a surface of the fluid,wherein the foam physically touches at least one of the pair ofconductive leads.